Non-linear optical properties, electrical conductivity and semiconductivity of organic semiconductor compounds have received attention in organic electronics and optoelectronics fields, and the development of various devices has been advanced actively. Typical examples of the organic semiconductor compounds include phthalocyanine compounds, porphyrin compounds and polyacenes. Properties such as non-linear optical properties, electrical conductivity and semiconductivity, which are required for using these compounds as organic materials to form devices, largely depend on crystallinity and orientation other than only purity of the materials. However, it has been difficult to highly purify these materials due to the reason that many compounds with extended π-conjugated systems are insoluble in solvents and susceptible to oxidation in air. In addition, a large-scale apparatus has been required for forming films, for example, a vacuum deposition apparatus for performing formation of a crystallized film with high orientation.
In recent years, organic field effect transistor (FET) devices using organic semiconductor compounds as the semiconductor layers have received attention. Organic semiconductor compounds, which show more flexible film properties compared with the properties of inorganic materials such as silicon, have been regarded as suitable materials for fabricating flexible devices using plastics as substrates.
However, as described above, pentacene and the like that are typical examples of organic semiconductor compounds are hardly soluble in solvents due to high crystallinity, so the formation of their films on substrates has only been possible by vacuum deposition. On the other hand, FETs are more easily fabricated by forming thin films by spin coating or the like from a solution of an organic semiconductor soluble in organic solvents. As an example of the above, π-conjugated polymers are used for semiconductor layers (Refer to “Japanese Journal of Applied Physics”, Japan Society of Applied Physics, Vol. 30, p. 596–598, 1991). In the case of π-conjugated polymers, it is known that the state of the orientation of molecular chains largely affects the electrical conductive properties. Similarly, it is reported that the field effect mobility of π-conjugated polymer field effect transistors largely depends on the state of the orientation of molecular chains in semiconductor layers (Refer to “Nature”, Nature Publishing Group, Vol. 401, P. 685–687, 1999).
However, since the molecular chains of π-conjugated polymers are oriented in a period between the coating of a solution and the drying of the same, there has been a possibility in which the state of the orientation of molecular chains largely varies depending on the change of environment or the difference of coating methods. There is also reported a FET using a film in which a soluble precursor thin film of pentacene is formed by coating and transformed to pentacene by heat-treatment (“Advanced Materials”, WILLEY-VCH Verlag GmbH, Vol. 11, p. 480–483, 1999). In this case, the conversion to pentacene has required a high-temperature treatment, and eliminated components with a large mass must have been removed under a reduced pressure.